The majority of retarded persons live with or under the supervision of their families for most of their lives. Despite a rapid growth in racial/ethnic minorities in the past decade, little attention has been paid to the impact of ethnic factors on the role of family caregiving for retarded persons. Prior research on Hispanics has been concerned with the effects of acculturation on a broad range of variables that include psychiatric and psychosocial adjustment as well as family organization, composition and functioning (Szapocznik & Herrera, 1978; Szapocznik & Kurtines, 1980). Given the central role that acculturation has played in research on adjustment of Hispanic families, the present study focuses on the impact of this variable on the families of adult mentally retarded Hispanics. It is likely that a significant number of Hispanics with a developmentally disabled member are not utilizing the service system because of problems with access that are due to the lack of cultural competence in the service delivery system. For these reasons, in the current study, considerable resources are dedicated to recruiting Hispanic subjects that may be outside of the formal service delivery system. The primary objective of this study is to investigate the moderating impact of acculturation on caregiver outcome and on the level of behavioral problems of the mentally retarded adult. A second, but closely related objective is to explore the cascading mechanisms by which acculturation influences changes in family functioning which in turn affect the ultimate outcomes. A third objective is to extend prior research on caregivers of mentally retarded adults to include their adult sibling caregivers. This study will extend our prior work on acculturation, its impact, and its mechanisms of action to a population of Hispanic families with a mentally retarded adult family member.